Badioreceiveb



I 4.9 I I I I I I I I I I I 49 I V I I I I I I INVENTOR DANIEL E. HARNETT ATTORNEYS D. E. HARNETT RADIORECEIVER Original Filed Dec. 14, 1931 Nov. 26, 1935.

M, 6M, 777% MW Reissued Nov. 26, 1935 UNITED STATES PATENT OFFICE IADIOBEOEIVEI DanielEHarnettflluckahoqHY adgnorto llaseltineOorporaiion No. 1,002,104, sues June 5, 1m, Serial Deeem ber 14, 1931.

Application for reissue October 3, 1935, Serlal No. 43,390

:1 Claims. zsc-ze) The present invention relates to an oscillator modulator, and, more particularly, to oscillator modulators for use in connection with superheterodyne radio receivers.

6 'In a superheterodyne receiver the signal or carrier frequency is converted into a ilxed intermediate frequency which may be amplified readily by specially designed amplifiers with practically uniform results regardless of the ire- 1o quency of the received signal. It is the usual practice to beat or modulate the incoming signal currents with locally produced currents oi a frequency differing from the frequency of the received signals by an approximately fixed amount.

15, This diiierence frequency is that to which the intermediate-frequency amplifiers are adapted to respond.

It has been proposed touse a single thermionic tube for the purposes of producing the locally 20 generated oscillations and modulating the incoming signal currents. However, as the frequency to which the receiver and oscillator circuits are tuned varies through a broad band, it

is diiilcult to produce an oscillator modulator 25 which will have suflicient output at all points within its tuning range and not have an output at some particular point which will result in overloading the grid circuit and thus cause the grid to draw current, the eilect of which is to reduce 30. the selectivity of the radio-frequency input circult, and cause cross-modulation between the desired and strong interfering signals.

It is the principal object of the present invention to produce an oscillator-modulator arrange- 35- ment which will have a substantially uniform translation gain throughout the entire tuning range.

It is a supplementary object of this invention to produce an oscillator-modulator circuit in 4,0, which the grid circuit of the modulator shall be free from overloading at any point within the t1tuninv1 g range in order to prevent loss of selecit is a still further object of the present invention to produce an oscillator-modulator arrangement in which the oscillatingcurrent is suppliedtothemodulatortubeinsuchamanner as to prevent the grid drawing current, which would i the selectivity of the tuned grid cir- 59 cuit, and prevent other overloading eii'ects.

These and further objects of the present invention will become apparent from the following specification when considered in connection with the accompanying drawing.

In accomplishing the objects of the present 5 invention, the oscillator modulator is provided with a unii'orm-gain oscillatory circuit so that the voltage output of said circuit, which eilects the grid circuit to produce the modulation of the received signals, will be substantially uniform throughout the tuning range of the oscillator. In other words,'a uniform-gain type oscillator permits the oscillator current to be limited to such a point that it does not paralyze the tube, and it is possible therefore to utilize it as an efllcient detector.

A uniform feed-back between an output electrode oi the oscillator-modulator tube is obtained by combining electromagnetic and electrostatic couplings in the proper phase so that a gain in the electromagnetic coupling is oflset by a decrease in the electrostatic coupling, and vice versa, as the circuit is tuned. The capacitive coupling may be obtained by a fixed condenser constituting a portion of the oscillation circuit. This condenser may have the dual function of assisting the alignment of the oscillation circuit with the input radio-frequency circuit to permit uni-control of these two circuits by the same. control element.

The oscillation circuit may be excited either from the plate or screen-grid electrodesby the use of appropriate connections.

Preferably, the oscillation circuit is electromagnetically coupled to an inductance placed in the cathode lead of the modulator-tube, by which it is meant that it is in a circuit which is common to the plate and grid circuits of the tube. In this event, the coupling is so chosen that the maximum voltage fluctuation of the rid relative to the cathode will be insuincient tocausethegridtoswingpositivesoastodraw current.

Alternatively, the oscillation circuit may be coupled to the plate circuit for excitation purposes and connected to an auxiliary grid of the tube for the purpose of varying the electron stream in the tube in accordance with the oscillation frequency and thus modulating the signal frequency impressed upon the grid circuit of the modulator. In this event, there is little dan-v ger of overloading the tube and no danger at all of causing the control grid to draw current, which would decrease the selectivity of the hiput circuit.

The cathode circuit may also include a selfbiasing resistor for maintaining the proper bias on the grid relative to the cathode, and if the value of this resistor is properly chosen, it may be caused to act as a regulator to prevent the modulator from overloading, as will be described hereinafter.

Attention is now invited to the drawing, in which:

Fig. 1 is a circuit showing an oscillator modulator arranged to oscillate between screen-grid and cathode; and

Fig. 2 is a similar circuitarranged to oscillate between plate and screen-grid.

Referring now more particularly to Fig. 1, a thermionic oscillator tube II is connected. as shown, to a tuned input circuit II, which includes inductance l5 and variable condenser I'I. Inductance I! may be inductively coupled to the inductance I9, which may be the output inductance of a radio-frequency amplifier or the antenna inductance of a receiver. The tuned grid circuit i3 is connected between ground and the grid of the tube ll through the usual grid-leak 22 shunted by condenser 28 for the purpose of producing grid modulation in the tube II, the grid-leak 22 and the inductance ll providing a conductive connection between grid and ground.

The output circuit of the tube ll comprises an output inductance 29, tuned by means of the adjustable condenser 31 to the intermediate frequency, and the high potential source ll. The condenser 31 and a condenser ll shunting the source I! are effective to by-pass high-frequency currents; that is, they provide a path to ground of negligible impedance to currents of signal or oscillation frequencies. The inductance 29 is inductively coupled to inductance 3|, included in the circuit 33, tuned by means of condenser to be resonant to the intermediate frequency. This circuit may be connected to an intermediate-frequcncy amplifier tube, which is not shown.

The oscillation circuit 42 includes the inductance 43, the adjustable condenser a, and the variable condenser 45. This circuit is coupled to the screen-grid circuit by means of the dual couplings provided between the inductance "I, included in said circuit, and the inductance l8. and the condenser 39, which is common to the screengrid and oscillation circuits;

For supplying the high voltages, there is provided the usual battery 49 connected through the inductance 29 to the plate of tube II. The screen-grid voltage is shown as being supplied by the connection to the battery ll through the isolating resistor 50. The specific means for supplying the screen and plate voltages constitute no part of the present invention, however. and

any appropriate method of voltage supply may uni-control arrangement of condensers l1 and 45. These tuned circuits are designed to have resonant frequencies differing by an amount substantially equal to the intermediate frequency.

The oscillation frequency is preferably the higher. The two tuning condensers I1 and ll generally have the same capacity variation. The oscillation frequency is made higher by making the inductance I! of lower inductance than coil Ii. With this change alone the frequency difference would vary in proportion to the resonant frequency of the signal input circuit. Therefore, the diiference at higher signal frequencies is decreased by making the effective minimum capacity of condenser I! and its associated circults slightly greater than that of condenser II and its associated circuits. Likewise, the difference at lower signal frequencies is increased by inserting the ilxed condenser is in series with the condenser ll. By proper choice of the oscillator elements ll, 38 and 43 relative to the signal circuit II, the frequency diiference is made exactly equal to the intermediate frequency at three pointsinthe tuningrange. This iscalled the alignment of signal and oscillation circuits to secure the intermediate-frequency difference. Padding condensers may be provided in parallel with either or both of the condensers I1 and II in order to permit adjustments for assisting in the alignment of the circuits l3 and 42.

The inductance ll is inductively coupled to the cathode inductance 24 for supplying the oscillation voltages to the input circuit of tube ll.

Although the resistance 22 and condenser 20 are shown as being included in the grid lead, they may; if desired, be included in the cathode lead instead, as shown in Fig. 2.

The operation of the circuit of Fig. 1 is as follows: The input circuit II is tuned to the incoming signal frequency and impresses upon the grid of the tube II a potential varying relative to the potential of the cathode II in accordance with the incoming signal. The resistance 22 and the condenser l are so arranged as to permit. grid modulation of the incoming signal by means of the oscillation volt g which is supplied from the oscillation circuit to the cathode of the modulator II. The oscillation voltage impressed upon the cathode of tube ll serves to vary the relative po- 46 tentials of the grid and cathode in accordance with the oscillation voltage. The tuned plate circuit 2! is adjusted to respond to the difference frequency, which is one of the components present in the output of the modulator II.

The screen-grid is utilized for supplying energy to the oscillation circuit, the coupling between the screen-grid and the oscillation circuit being the dual couplings provided by the inductance between inductances U and ll and the capacity of i6 condenser II. The inductive coupling is so arranged that it will increase with an increase in the frequency oscillations;- whereas the impedance of the condenser is being less at high freouencies, the electrostatic coupling will decrease. U The electromagnetic coupling, on the other hand. decreases at the low frequencies. and the impedance of the condenser 38 increases at the low frequencies. Thus, a substantially uniform coupling between the output or screen electrode may be ll provided which will cause a substantially uniform voltage to be produced by the oscillation circuit 42 regardlem of the frequency to which it is tuned.

Whereas Fig. 1 shows a circuit in which the oscillation circuit is excited by means of the '70 screen-grid, it is obvious. of course, that this excitation may be from the plate circuit if desired.

An alternative means of accomplishing the principal object of the present invention is illustrated in Pig. 2, to which attention is now inis ropes 3 vited. Inthisflgureinwhichlihepartsare designated by similar reference numerals, the modulator II has a tuned grid circuit i3, a tuned plate circuit 23, and an oscillation circuit 4!. The grid circuit includes the inductance Ii and the variable condenser l1 and is inductively coupled to the inductance I, which may be the output inductance of a radio-frequency amplifier or the antenna inductance of the radio receiver. The grid circuit is connected to the grid and cathode, the latter connection being through the selfbiasing resistor 23, which is shunted by the usual bY-pass condenser 23. This resistor has, in addition to the usual function of producing the bias on the grid relative to the cathode, the function of regulating and limiting the plate voltage. The resistor is included not only in the grid circuit, but in the plate circuit, and thus an increase in the grid voltage, which might tend to overload the modulator, results in increased plate current and a change in the bias of the grid in the direction to reduce the plate current.

The plate circuit includes the tuned output circuit II, which is connected to the high potential source l3, shunted by the radio-frequency by-pass condenser ll.

For exciting the oscillation circuit 42, it is coupled through adjustable condenser 33 to the plate circuit. The coupling between the plate and oscillation circuits is of the uniform-gain type, which has just been described in connection with Fig. 1 and therefore the description of this arrangement will not be repeated here.

The oscillationcircuit 42 is directly connected to an auxiliary grid of the oscillator-modulator tube II, as shown, whicharrangementserves to impress an oscillation voltage upon this grid of the oscillation frequency This varying voltage serves to effect the plate impedance of the tube and thereby modulates the-signal current impressed through the tuned circuit I3 on the tube The uniform-gain characteristics of the oscillation circuit are useful in this arrangement in preventing the plate current from varying to such an extent as to cause distortion or overload the plate circuit.

The condensers 35, 36, 31 and 39 are each made adjustable. Condensers 35 and 31 are adjusted to tune the circuits and a: m the intermediate scribed do not constitute any part of the present invention. These constants are variable within limits to accomplish the results indicated above.

It is to be understood that whereas the oscillator modulator embodying this invention is vprimarily for the purpose of superheterodyne radio receivers in which the grid circuit is coupled to the input of a radio receiver or the output of a radio-frequency amplifier tube and the plate circult of the oscillator modulator is coupled to an intermediate-frequency tuned circuit, the oscillator modulator described may be utilised in any other suitable connection, and its use, therefore.

inasuperheterodyneisnottobe construedasa limitation of the invention.

Furthermore, whereas the above-noted improvements have been found especially useful in radio-frequency circuits, it is to be understood 5 that the principles involved are equally applicable for use in connection with vacuum tube circuits operating at any desired frequency. Also, the principles involved may be useful in connection with hetercdyne, self-heterodyne or autodyne 1o methods of receiving radio-frequency signals in which the oscillator modulator produces an audio beat. Similarly, the elements constituting the present invention may be utilized in connection with a homodyne or zero beat receiver. Oscillal6 tors of this may be readily synchronized when tuned approximately to a master oscillator or to a harmonic of a master omiliator.

What is claimed is:

l. Anoscillator-modulator circuit including a :0 tube having input electrodes including a common electrode, and output electrodes including said common electrode, a tunable circuit connected to one of said input electrodes and adapted to respond to the frequency of currents which it is 23 desired to modulate, an inductance connected between said tunable circuit and said common electrode, a grid condenser connected between said tunable circuit and one of said input electrodes and a grid-leak connected effectively between sa d input electrodes, an oscillation circuit tuned to respond to a frequency differing from that of the first-mentioned circuit by a fixed amount and including an inductance, inductively related to said first-mentioned inductance, and a coupling between said oscillation circult and an output electrode of said tube, whereby the currents of the frequency to which said tunable circuit responds are modulated by the currents produced by said oscillation circuit;

2. An oscillator-modulator circuit including a tube having input electrodes including a common electrode and output electrodes including said common electrode, a tunable circuit connected to one of said input electrodes and adapted to respond to the frequency of currents which it is desired to modulate, an inductance connected between said tunable circuit and said common electrode, a grid condenser connected between said tunable circuit and one of said input electrodes and a grid-leak connected effectively between said input electrodes, an oscillation circuit tuned to respond to a frequency differing from that of the first-mentioned circuit by a fixed amount and including an inductance, inductively related to said first-mentioned inductance, a coupling between said oscillation circuit and an output electrode of said tube, whereby the currents of the frequency to which said tuned circuit responds are modulated by the currents produced by said oscillation circuit, and an output circuit also connected to an output electrode and tuned to respond to the difference between the frequencies of said tunable circuit and said oscillationcircuit.

3. An oscillator-modulator circuit including a tube having input electrodes including a common electrode, and output electrodes including said common electrode, a tunable circuit including a variable condenser connected to one of said input electrodes, an inductance connected between said tunable circuit and said common electrode, an oscillation circuit including an inductance and a variable condenser, said lastmentioned inductance being inductively related to said first-mentioned inductance, a coupling between said oscillation circuit and an output electrode, a tuned output circuit connected to an output electrode and tuned to the frequency difference between said tunable circuit and said oscillation circuit, means for simultaneously timing said tunable circuit and said oscillation circuit. and means for permitting a constant frequency difference to be maintained between said circuits as they are simultaneously timed.

4. An oscillator-modulator circuit including a tube having input electrodes including a common electrode, and output electrodes including said common electrode, a tunable circuit including an inductance and a variable condenser connected to one of said input electrodes, an inductance connected between said tunable circuit and said common electrode, an oscillation circuit including a portion of a third inductance and a variable condenser, said last-mentioned inductance being inductively related to said first-mentioned inductance. a coupling between said oscillation circuit and an output electrode, a tuned output circuit connected to an output electrode and tuned to the frequency difierence between said tunable circuit and said oscillation circuit, means for simultaneously tuning said timable circuit and said oscillation circuit, and means for maintaining a constant frequencydiiference between said circuits as they are simultaneously tuned, said last-mentioned means including a condenser connected to a tap on said third-mentioned inductance and to said common electrode through said second-mentioned inductance.

5. An oscillator-modulator circuit including a tube having cathode, anode and two or more grid electrodes. a tuned circuit including an inductance and a variable condenser connected between said cathode and one of said grid electrodes. an oscillation circuit including an inductanoe and a variable condenser connected to another of said grid electrodes and coupled to said anode, and means for simultaneously tuning said tuned circuit and said oscillation circuit, whereby a substantially constant difference frequency is maintained between the frequency to which said tuned input circuit responds and that to which said oscillation circuit responds as said tube oscillates between anode and one of said grid electrodes and thus modulates currents of the frequency to which said input circuit is tuned, by the omillation frequency.

6. An oscillator-modulator circuit including a thermionic tube having input electrodes, output electrodes, and a screen electrode, a tuned circuit including an inductance and a variable condenser connected to an input electrode, an oscillation circuit including an inductance and a variable condenser connected to said screen electrode and coupled to an output electrode. means for simultaneously tuning said tuned circuit and said oscillation circuit, whereby a substantially constant difference frequency is maintained between the frequency to which said tuned input circuit responds and that to which said oscillation circuit responds as said tube oscillates between the output and screen electrodes and thus modulates currents of the frequency to which said input circuit is tuned by the oscillation frequency, and a second tuned circuit connected to said output electrode and tuned to the difference between the frequencies to which said input andoscillation circuits respond.

7. An oscillator-modulator circuit including a thermionic tube having input electrodes. output electrodes,andascreenelectrode,atunedcircuit including an inductance and a variable r connected to an input electrode, an oscillation circuit including an inductance and a variable condenser connected to said screen electrode and coupled to an output electrode, means for simul-- s taneously tuning said tuned circuit and said oscillation circuit, whereby a substantially constant diiference frequency is maintained between the frequency to which said tuned input circuit responds and that to which said oscillation circuit 10 assaid tubeosciliatesbetweentheoutput and screen electrodes and thus modulates currents of the frequency to which said input circuit is tuned by the oscillation frequency. a second tuned circuit connected to an output electrodil it and tuned to the difference between the frequencies to which said input and oscillation circuits respond, and means for simultaneously permitting said input and oscillation circuits to respond to frequencies diifering from each other 20 by a substantially fixed amount and providing dual couplings between said output electrode and said oscillation circuit.

8. An oscillator system tunable over a frequency range, comprising a vacuum tube having at least three electrodes, a connection between one of said electrodes and ground, a main coil having one end coupled to another of said electrodes a variable tuning condenser connected between ground and the other end of said main coil, a. fixed coupling condenser connected between ground and an intermediate point on said coil. and an auxiliary coil coupled to said main coil and connectedbetween ground and a third of said electrodes.

9. An oscillator system tunable over a frequency range, comprising a vacuum tube having a cathode and at least two other electrodes, a connection between one of said electrodes and ground, amain coil havingoneendcoupledtoio another of said electrodes, a variable tuning condenser connected between ground and the other end of said main coil, a fixed coupling condenser connected between ground and an intermediate point on said coil, and a auxiliary coil coupled to said main coil and connected between ground and said cathode.

10. An oscillator system tunable over a frequency range, comprising a vacumn tube having an input electrode, output electrodes, and a common electrode. a connection between said input electrode and ground, a main coil having one end coupled to one of said output electrodes, a variable tuning condenser connected between ground andthe otherendcfsaidmaincoil,afixedcondenser connected between ground and an intermediate point on said coil, and an auxiliary coil coupled to said main coil and connected between ground and said common electrode.

-ll.An oscillator system timable over a fro-o0 quency range, comprising a vacuum tube having cathode, grid and at least one other electrode, a connection between said grid and ground, a main coil having one and coupled to said other electrode. a variable tuning condenser connected beso tweengroundandtheotherendofsaidmain coil, a fixed condenser connected between ground and an intermediate point on said coil, and an auxiliarycoilcmipledtosaidmain coilandconnected between ground and said cathode.

ilanoscillatorsystemtimable over-afrequency range, comprising a vacuum tube having cathode, grid, screen and plate electrodes, a connection between saidgrid and ground, apath betweenoneofsaidscreenandplateelectrodssll ropes 5 cathode,gridandatleastoneotherelectrode, aconnectionbetweensaidgridandgrotmda maincoilhaving twosectionsconductivelyconnected and electromagnetieally coupled together, one end ofsaid maincoilbeingcoupledtosaid otberelectrode,avariabletuningcondenserconnectedbetweengrcimdandtheotherendofsaid maincoiLafixedcouplingconnectedbetween ground and the point between said main coil sections, and an auxiliary coil coupled to said main coil and connected between ground and said cathode, said coupling condenser and the section of the main coil coupled to said other electrode being proportioned to maintain a predetermined relation between amplitude and frequency of the oscillations.

14. In a combined oscillator modulator, an electron discharge tube having a plurality of electrodes, a tunable oscillation circuit, tunable input and tuned output circuits connected to said electrodes, a dual coupling from one of said electrodes to said oscillation circuit, said coupling including one portion,. the reactanee of which increases with frequency, and a second portion, the reactance of which decreases with frequency by a substantially corresponding amount, whereby a substantially uniform amplitude of oscillations is obtained, and a coupling between said oscillation circuit and an input electrode of said device.

15. An oscillator system tunable over a frequency range, comprising a vacuum tube having cathode, grid and at least one other electrode, a main coil having one end coupled to said other electrode, a variable tuning condenser connected between ground and the other end of said main coil, a fixed condenser connected between ground and an intermediate point on said coil, an auxiliary coil coupled to said main coil and connected between ground and said cathode, and a tuned circuit connected between said grid and ground and tuned to a frequency differing from the frequency of the oscillations produced by said oscillator, by a fixed amount.

16. An oscillator system tunable out a frequency range, comprising a vacuum tube having cathode. grid and at least two other electrodes, a main coil having one end coupled to one of said other electrodes, a variable tuning condenser connected between ground and the other end of said main coil, a fixed condenser connected between ground and an intermediate point on said coil, an auxiliary coil coupled to said main coil and connected between ground and said cathode, a tuned circuit connected between said grid and ground and tuned to a frequency diifering from the frequency of the oscillations produced by said oscillator, by a fixed amount, and a tuned output circuit connected to one of said other electrodes and tuned to the fixed diiference frequency.

i'LAn oscillatorsystemtunable overafrequency range, comprising a vacuum tube having cathode, grid andatleastoneotherelectrode,a

main coil having one end coupled to said other electrode, a variable tuning condenser connected betweengroundandtheotherendofsaidmain coil, afixedcondenserconnectedbetweenground andanintermediatepointonsaidcoihanauxfl- 5 iary coil coupled to said main coil and connected between ground and said cathode, a tuned circuit connected between. said grid and ground and tunedtoafrequencydiiferingfromthefrequsney ofthe oscillationsproducedbysaidosciliatonby a fixed amount, and means for simultaneously tuning both of said circuits.

18.An0scillator systemtunableoverafrequency range, comprising a vacuum tube having cathode, grid and at least two other electrodes, 15 amaincoilhavingoneendcoupledtooneot said other electrodes, a variable tuning condenser connected between ground and the other end of said main coil, a fixed condenser connected between ground and an intermediate point on said go coil, an auxiliary'coil coupled to said main coil and connected between ground and said cathode, a tuned circuit connected between said grid and ground and tuned to a frequency diifering from the frequency of the oscillations produced by said 5 oscillator, by a fixed amount, means for simul taneously tuning both of said circuits, and a tuned output circuit connected to one of said other electrodes and permanently tuned to the fixed difference frequency. w

19. In a superheterodvne' receiver, an oscillator-modulator circuit including an electron discharge tube having input and output electrodes, an input circuit for said device tunable to respond to any frequency within a frequency band, 5 an oscillation circuit including a fixed condenser and tunable to respond to a frequency differing from the frequency to which said input circuit is tuned, by a substantially constant amount, simultaneous actuating means for tuning both ,of said circuits, a coupling between an output electrode of said tube and said oscillation circuit,

said coupling including a fixed condenser of said circuit which assists in the alignment of said circuit with said input circuit as said circuits are 5 tuned throughout the frequency band. 7

20. In a superheterodyne receiver, an oscillator-modulator arrangement comprising athermionic tube having input and output electrodes, a tuned input circuit connected to one of said input 50 electrodes and having a variable condenser for varying the frequency to which said circuit is tuned, an oscillation circuit coupled to one of the output electrodes of said device and connected to said input circuit, said oscillation circuit includ- 55 ing a variable condenser for varying the frequency of the oscillations of said circuit throughout a range of frequencies, means for simultaneously varying both of said condensers, a fixed series condenser in said oscillation circuit for causing go the frequency of the current produced thereby to differ from the frequency of said input circuit by a substantially constant amount as said circuits are simultaneously tuned, and a dual coupling between the output of said thermionic device .and as said oscillation circuit, said coupling including an inductive coupling and said series condenser, and said couplings being so arranged that the voltage produced by said circuit is substantially uniform throughout the range of frequencies, 7

21. In a superheterodyne receiver, an oscillator-modulator arrangement comprisinga thermionic tube having input, output, and common electrodes, a tuned input circuit for said tube including a variable condenser, an oscillation ciru 

